Arrival/Departure Tower Separation in Low Cloud Conditions
I'd like to know what separation any tower units apply between Departures and Arrivals in Low Cloud (let's say OVC at 200ft) and what justification you have for that...e.g. MATS 2 entries.
Scenario:
Arrival aircraft at 4.5nm final. You line up a departure. You clear departure for take-off as arrival reaches about 3nm final. Given the low cloud you are not visual with the arrival.
The departure gets airborne in about 40seconds. By this time the arrival is about 1.5nm from touchdown. You clear it to land. The departure quickly disappears into cloud and the arrival is still not visible.
(1) What separation are you providing? (Both aircraft are not visible and you have less than standard separation)
(2) What allows you to do this? (Please provide references)
Thanks